1. Field of the Invention
The present invention relates to a communication device and method for operating the communication device in a redundant industrial communication network.
2. Description of the Related Art
In distributed industrial automation systems, when registering, evaluating and communicating measurement and control data, it is necessary to ensure that complete and unchanged data are present in real time particularly in the case of time-critical industrial production processes. Intentional changes, unintentional changes or changes caused by a technical fault are to be avoided because within an industrial automation system, this can lead to inconsistent system states and system failures with economically serious outage times.
In addition, interruptions of communication connections between computer units of an industrial automation system can lead to an undesirable or unnecessary repetition of a communication of a service request. This causes an additional capacity utilization of communication connections of the industrial automation system, which can lead to further system disturbances or faults. A particular problem area in industrial automation systems regularly results from message traffic with comparatively many, but relatively short messages, as a result of which the above problems are intensified.
In order to be able to compensate for failures of communication connections or devices, communication protocols such as high-availability seamless redundancy or parallel redundancy protocol have been developed for high-availability, redundantly operable industrial communication networks. High-availability seamless redundancy (HSR) and parallel redundancy protocol (PRP) are defined in the International Electrotechnical Commission Standard (IEC) 62439-3 and enable hitless redundant transmission of data packets with extremely short recovery times. In accordance with high-availability seamless redundancy and parallel redundancy protocol, each data packet is duplicated by a transmitting communication device and sent to a receiver on two different paths. Redundant data packets representing duplicates are filtered out of a received data stream by a communication device at the receiver ends.
DE 10 2008 017 192 A1 describes a method for establishing a network comprising a first network subscriber having a set of ports. The ports are connected to ports of further network subscribers of the network. In a first method step, the ports assigned to the first network subscriber are switched into a first operating mode. In the first operating mode, test messages can be received and transmitted via the ports. In accordance with a further method step, test messages are transmitted via the ports assigned to the first network subscriber. Furthermore, the ports assigned to the first network subscriber are switched into a second operating mode if no test message of the transmitted test messages is received again by the first network subscriber. In the second operating mode, messages received via one of the ports assigned to the first network subscriber are forwarded via the remaining ports. In this way, it is possible to avoid formation of network loops when internetworking or extending complex networks.
EP 2 282 452 A1 describes a method for data communication within a ring-link communication network, where the data communication is effected in accordance with high-availability seamless redundancy and the communication network comprises at least one master node, a source node and a destination node. Each node has a first and a second communication interface with a respective first and second neighboring node. Furthermore, each node receives data frames via the first communication interface and forwards the received data frame either changed or unchanged via the second communication interface without additional delay. The master node transmits a first and second redundant data frame or an empty data packet to its first and second neighboring node, respectively. Upon reception of the two redundant data frames, the source node fills the respective data frame with process data in a predetermined reserved area. Afterward, each filled data frame is immediately and individually forwarded to the first and second neighboring node of the source node, respectively. The destination node further extracts the process data from the first received filled data frame of a pair of redundant data frames.
EP 2 343 857 A1 describes a network node for a communication network comprising a first sub-network and a second sub-network, which is connected to the first sub-network. While data transmission is effected in accordance with a spanning tree protocol in the first sub-network, a second protocol, which differs from the protocol used in the first sub-network is used for data transmission in the second sub-network. The network node described in EP 2 343 857 A1 is designed as an element for the second sub-network and for communication within the second sub-network. Furthermore, the network node is designed, by means of spanning tree functionality, as a spanning tree main node for monitoring and controlling the second sub-network. As a result, the second sub-network can be handled as a virtual network node by the spanning tree protocol used in the first sub-network.
EP 2 413 538 A1 discloses a method for redundant communication in a communication system comprising a plurality of communication networks. The communication networks are connected to one another via at least one coupling node. Data originating from a first communication network are prevented from being transmitted back from a second communication network into the first communication network based on information defined prior to data transmission.